As noted, processes and compositions for the reduction of nitrogen oxides in effluents from the combustion of carbonaceous fuels have been developed extensively over recent years. With the increased attention to the health risks and environmental damage caused by agents such as smog and acid rain, it is expected that NO.sub.x reduction research will continue to be pursued.
In the past, most SNCR processes for reducing nitrogen oxides levels have concentrated on achieving maximum NO.sub.x reductions without addressing the problems raised by the production of other pollutants, such as ammonia and carbon monoxide. More recently, in a unique application of nitrogen oxides reducing principles, Epperly, Peter-Hoblyn, Shulof, Jr., and Sullivan, in U.S. Pat. No. 4,777,024, disclose a method of achieving substantial nitrogen oxides reductions without the production of a major amount of other pollutants through a multiple stage treatment agent injection process. Although minimizing the production of other pollutants, this process, like any process which involves the high temperature introduction of nitrogenated compounds such as urea or ammonia, will still generate some other pollutants.
This is also the case with the method of U.S. Pat. No. 4,780,289, issued to Epperly, O'Leary and Sullivan, which discloses another method for maximizing NO.sub.x " reductions while minimizing other pollutants. Although minimized, such other pollutants are still present.
In U.S. Pat. No. 4,302,431, Atsukawa et al. disclose a process for nitrogen oxides reduction involving introducing ammonia into an exhaust gas at 700.degree. C. (1292.degree. F.) to 1300.degree. C. (2372.degree. F.), and then passing the exhaust gas over a catalyst at a temperature between 300.degree. C. (572.degree. F.) and 500.degree. C. (932.degree. F.) (preferably with the introduction of additional ammonia) to decompose remaining NO.sub.x and ammonia. This process, though, involves the introduction of ammonia into the exhaust gas with the concommitant toxicity and handling problems of ammonia.
What is desired, therefore, is a process for nitrogen oxides reduction which can achieve substantial reductions in NO.sub.x while avoiding the emission of other pollutants and without the necessity for storage and handling of ammonia.